1. The Field of the Invention
The present invention relates to the manufacture of fuel cell electrodes. More particularly, the present invention relates to the manufacture of electrodes having highly dispersed nanoparticles manufactured from complexed catalyst atoms.
2. Related Technology
Particle catalysts are an important component of fuel cells. The catalyst is incorporated into the electrode of each half cell to increase the rate of the reactions in the fuel cell. Improving catalyst performance can increase power output of a fuel cell, reduce the size of the fuel cell, and/or allow the fuel cell to operate at lower temperatures. Because fuel cells are typically made from precious metals such as platinum and ruthenium, improvements in catalyst performance can also significantly reduce the cost of the fuel cell.
Performance of fuel cell catalysts has typically been improved by reducing the size of the catalyst particles. Particulate catalysts are only active at the surface. Reducing the size of the catalyst particles increases the surface to weight ratio, thereby increasing catalyst performance. Recent improvements in techniques for manufacturing particle catalysts have enabled formation of nanoparticles having an average size of less than 5.0 nm. Even at these extremely small sizes, there is still a significant amount of metal that is not exposed on the outer surface, resulting in low metal utilization. For example, 2.5 nm platinum particles in a face centered cubic (“fcc”) crystal structure utilizes about 45% of the platinum atoms, whereas a 5.0 nm particle utilizes only about 23% of the platinum atoms. Therefore, to reach nearly atomic dispersion, the average particle size of the metal needs to be 2.5 nm or less, typically 1.5 nm or less.
One problem with making and maintaining particles less than 2.5 nm is particle stability. Particle stability is known to depend on particle surface area. As the surface area increases, the particle surface energy also increases, which can cause agglomeration of the catalyst particles. At particle sizes of 2.5 nm or less the surface energy is very high and catalyst made using existing methods agglomerate to form lager particles.